Millions of people take medicine that might make the flu vaccine less effective

AP (Reuters Health) - Millions of people who take statins to lower cholesterol may not get maximum protection from flu vaccines, two new studies suggest.

Both studies looked at the effectiveness of flu vaccines in people who were or were not using statins. Taken together, the results connect statins to a dampened immune response to flu vaccines and greater odds of respiratory infections during flu season.

The findings, published in the Journal of Infectious Diseases, pose a particular conundrum for the elderly, who are more likely to die or face serious complications from the flu and also more likely to take statins to prevent potentially fatal heart attacks and strokes.

But until more research confirms exactly how statins interact with the vaccines, older patients should stay the course with both their medications and vaccinations, said Dr. Robert Atmar, an infectious disease researcher at Baylor College of Medicine and Ben Taub General Hospital in Houston who wrote an editorial accompanying the studies.

"Statins shouldn't be stopped because they already have been shown to lead to significant benefits such as decreased mortality due to cardiovascular events," Atmar said by email. "Patients should also continue to get vaccinated against influenza because it is still the best way to prevent getting sick."

In one of the studies, researchers analyzed data on how well more than 5,000 people over 65 responded to different versions of the flu vaccine during the 2009-2010 and 2010-2011 flu seasons in the U.S., Colombia, Panama and the Philippines.

About three weeks after getting vaccinated, the people who didn't take statins produced 38 percent to 67 percent more antibodies against the influenza virus than people who used the cholesterol drugs.

Since statin use wasn't randomly assigned, it's possible that the diminished effectiveness of the flu vaccines might be due to other factors, acknowledge the authors, who are affiliated with Novartis, a leading flu vaccine manufacturer.

"We felt the studies are important to bring this issue into the open so that the results can be verified by others and, most importantly, strategies can be developed to optimally protect this high risk group against influenza," said lead study author Steven Black, of the Center for Global Health at Cincinnati Children's Hospital in Ohio.

It's possible that pausing statin use for a period of time prior to immunization might help prevent the diminished effectiveness of the flu shots, though that might be risky for heart disease and stroke, Black said by email.

Another strategy might be giving more potent or multiple doses of the vaccine to statin users, though this might be logistically challenging, Black added.

For the second study, researchers examined rates of respiratory infections linked to influenza from 2002 to 2011 among people 45 and older who got health care through Kaiser Permanente in Georgia.

The effectiveness of the vaccine in protecting against these infections was 26.2 percent for people not on statins, but just 12.6 percent among those using the cholesterol drugs.

Because respiratory infections can be caused by bacteria and viruses other than influenza, it's possible that not all cases found in the study were connected to the flu. The researchers acknowledge in their report that they didn't have lab tests confirming an influenza diagnosis.

Still, it's biologically plausible that statins may make the flu vaccine less effective, said lead study author Saad Omer of Emory University in Atlanta.

"It's important to remember that even with somewhat diminished effectiveness, the flu shot remains the best tool to prevent influenza in the elderly," Omer said by email.